This invention pertains to the treatment of hydrocarbon solutions of hydrocarbon-soluble organomagnesium compounds, particularly dialkylmagnesium compounds.
Organomagnesium compounds of the dialkylmagnesium type are prepared in general by reaction of magnesium metal with one or more alkyl halides (according to the nature of the desired product); the process is generally conducted in a hydrocarbon solvent. Such dialkylmagnesium compounds have the general formula R.sub.2 Mg in which the groups R may be identical or different alkyl groups. Not all dialkylmagnesium compounds having this general formula, however, are hydrocarbon soluble. Compounds such as dimethyl-, diethyl-, dipropyl- and di-n-butylmagnesium are not hydrocarbon soluble. On the other hand, compounds having C.sub.5 alkyl or higher groups attached to the magnesium are hydrocarbon soluble. Additionally, some compounds having a mixture of lower alkyl groups attached to the magnesium are hydrocarbon soluble. These include n-butylethylmagnesium (U.S. Pat. No. 4,127,507), n-butylmethylmagnesium (U.S. Pat. No. 4,222,969) and n-propylmethylmagnesium (U.S. Pat. No. 4,207,207).
When hydrocarbon soluble dialkylmagnesium products are prepared by the reaction of alkyl halides with metallic magnesium in a hydrocarbon solvent, solids are formed which may be recovered by conventional techniques such as centrifugation, decanting or filtration. These solids comprise primarily magnesium chloride and unreacted magnesium metal. The resulting hydrocarbon solution of the dialkylmagnesium can then be diluted or concentrated as desired, depending on the ultimate concentration desired for purposes of reactivity, viscosity or economic considerations. If the solution is viscous, a viscosity reducing agent such as a trialkylaluminum compound may be included.
However, it has now been discovered that additional solids may later form in the thus separated hydrocarbon solution of dialkylmagnesium by post-precipitation when the product is stored. The post-precipitation may occur from several days to several weeks after recovery of the product solution following filtration, decantation or centrifugation. This post-precipitation results in turbidity in the product solution and can lead to decreased activity of the product due to the presence of very fine suspended solid particles.
The solids formed by post-precipitation can be removed by permitting the product to stand in storage for a sufficient time to precipitate these later formed solids, followed by a final filtration step just prior to shipping the product. Such a technique can produce stable, clear solutions, but this requires the product to be held in storage for a period of at least several additional weeks before shipping, and the final filtration involves additional processing which, of course, increases the cost of production.